Clearing the map in the final mission "All In" in StarCraft II: Wings of Liberty.Check out some of my other full game speedruns:StarCraft Broodwar Remastered...

tl;dw: The player massed a campaign-only building that allows you to mind-control Zerg, which he used to convert mutalisks and broodlords until he had a giant army of 250+ mutalisks when he then proceeded to go on a huge rampage